I'm no gearbox expert, but I do know that even in neutral, with your foot off the clutch (therefore the clutch plate engaged to flywheel), the front shaft in the gearbox is spinning. Basically all gearboxes are the same. It sounds like the thrust bearing, which is something you replace when doing the clutch, not necessarily a gearbox reconditioning, or it can be done by itself if it's really a problem cos it will still involve removing the gearbox obviously.